/*
 * avl_tree.h - intrusive, nonrecursive AVL tree data structure (self-balancing
 *              binary search tree), header file
 *
 * Written in 2014-2016 by Eric Biggers <ebiggers3@gmail.com>
 * Slight changes for compatibility by Ben Kurtovic <ben.kurtovic@gmail.com>
 *
 * To the extent possible under law, the author(s) have dedicated all copyright
 * and related and neighboring rights to this software to the public domain
 * worldwide via the Creative Commons Zero 1.0 Universal Public Domain
 * Dedication (the "CC0").
 *
 * This software is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the CC0 for more details.
 *
 * You should have received a copy of the CC0 along with this software; if not
 * see <http://creativecommons.org/publicdomain/zero/1.0/>.
 */

#ifndef _AVL_TREE_H_
#define _AVL_TREE_H_

#include <stddef.h>

#if !defined(_MSC_VER) || (_MSC_VER >= 1600)
#    include <stdint.h>
#endif

#ifdef __GNUC__
#    define AVL_INLINE inline __attribute__((always_inline))
#elif defined(_MSC_VER) && (_MSC_VER < 1900)
#    define AVL_INLINE __inline
#else
#    define AVL_INLINE inline
#endif

/* Node in an AVL tree.  Embed this in some other data structure.  */
struct avl_tree_node {

    /* Pointer to left child or NULL  */
    struct avl_tree_node *left;

    /* Pointer to right child or NULL  */
    struct avl_tree_node *right;

    /* Pointer to parent combined with the balance factor.  This saves 4 or
     * 8 bytes of memory depending on the CPU architecture.
     *
     * Low 2 bits:  One greater than the balance factor of this subtree,
     * which is equal to height(right) - height(left).  The mapping is:
     *
     * 00 => -1
     * 01 =>  0
     * 10 => +1
     * 11 => undefined
     *
     * The rest of the bits are the pointer to the parent node.  It must be
     * 4-byte aligned, and it will be NULL if this is the root node and
     * therefore has no parent.  */
    uintptr_t parent_balance;
};

/* Cast an AVL tree node to the containing data structure.  */
#define avl_tree_entry(entry, type, member)                                            \
    ((type *) ((char *) (entry) -offsetof(type, member)))

/* Returns a pointer to the parent of the specified AVL tree node, or NULL if it
 * is already the root of the tree.  */
static AVL_INLINE struct avl_tree_node *
avl_get_parent(const struct avl_tree_node *node)
{
    return (struct avl_tree_node *) (node->parent_balance & ~3);
}

/* Marks the specified AVL tree node as unlinked from any tree.  */
static AVL_INLINE void
avl_tree_node_set_unlinked(struct avl_tree_node *node)
{
    node->parent_balance = (uintptr_t) node;
}

/* Returns true iff the specified AVL tree node has been marked with
 * avl_tree_node_set_unlinked() and has not subsequently been inserted into a
 * tree.  */
static AVL_INLINE int
avl_tree_node_is_unlinked(const struct avl_tree_node *node)
{
    return node->parent_balance == (uintptr_t) node;
}

/* (Internal use only)  */
extern void avl_tree_rebalance_after_insert(struct avl_tree_node **root_ptr,
                                            struct avl_tree_node *inserted);

/*
 * Looks up an item in the specified AVL tree.
 *
 * @root
 *      Pointer to the root of the AVL tree.  (This can be NULL --- that just
 *      means the tree is empty.)
 *
 * @cmp_ctx
 *      First argument to pass to the comparison callback.  This generally
 *      should be a pointer to an object equal to the one being searched for.
 *
 * @cmp
 *      Comparison callback.  Must return < 0, 0, or > 0 if the first argument
 *      is less than, equal to, or greater than the second argument,
 *      respectively.  The first argument will be @cmp_ctx and the second
 *      argument will be a pointer to the AVL tree node of an item in the tree.
 *
 * Returns a pointer to the AVL tree node of the resulting item, or NULL if the
 * item was not found.
 *
 * Example:
 *
 * struct int_wrapper {
 *      int data;
 *      struct avl_tree_node index_node;
 * };
 *
 * static int _avl_cmp_int_to_node(const void *intptr,
 *                                 const struct avl_tree_node *nodeptr)
 * {
 *      int n1 = *(const int *)intptr;
 *      int n2 = avl_tree_entry(nodeptr, struct int_wrapper, index_node)->data;
 *      if (n1 < n2)
 *              return -1;
 *      else if (n1 > n2)
 *              return 1;
 *      else
 *              return 0;
 * }
 *
 * bool contains_int(struct avl_tree_node *root, int n)
 * {
 *      struct avl_tree_node *result;
 *
 *      result = avl_tree_lookup(root, &n, _avl_cmp_int_to_node);
 *      return result ? true : false;
 * }
 */
static AVL_INLINE struct avl_tree_node *
avl_tree_lookup(const struct avl_tree_node *root,
                const void *cmp_ctx,
                int (*cmp)(const void *, const struct avl_tree_node *))
{
    const struct avl_tree_node *cur = root;

    while (cur) {
        int res = (*cmp)(cmp_ctx, cur);
        if (res < 0) {
            cur = cur->left;
        } else if (res > 0) {
            cur = cur->right;
        } else {
            break;
        }
    }
    return (struct avl_tree_node *) cur;
}

/* Same as avl_tree_lookup(), but uses a more specific type for the comparison
 * function.  Specifically, with this function the item being searched for is
 * expected to be in the same format as those already in the tree, with an
 * embedded 'struct avl_tree_node'.  */
static AVL_INLINE struct avl_tree_node *
avl_tree_lookup_node(const struct avl_tree_node *root,
                     const struct avl_tree_node *node,
                     int (*cmp)(const struct avl_tree_node *,
                                const struct avl_tree_node *))
{
    const struct avl_tree_node *cur = root;

    while (cur) {
        int res = (*cmp)(node, cur);
        if (res < 0) {
            cur = cur->left;
        } else if (res > 0) {
            cur = cur->right;
        } else {
            break;
        }
    }
    return (struct avl_tree_node *) cur;
}

/*
 * Inserts an item into the specified AVL tree.
 *
 * @root_ptr
 *      Location of the AVL tree's root pointer.  Indirection is needed because
 *      the root node may change as a result of rotations caused by the
 *      insertion.  Initialize *root_ptr to NULL for an empty tree.
 *
 * @item
 *      Pointer to the `struct avl_tree_node' embedded in the item to insert.
 *      No members in it need be pre-initialized, although members in the
 *      containing structure should be pre-initialized so that @cmp can use them
 *      in comparisons.
 *
 * @cmp
 *      Comparison callback.  Must return < 0, 0, or > 0 if the first argument
 *      is less than, equal to, or greater than the second argument,
 *      respectively.  The first argument will be @item and the second
 *      argument will be a pointer to an AVL tree node embedded in some
 *      previously-inserted item to which @item is being compared.
 *
 * If no item in the tree is comparatively equal (via @cmp) to @item, inserts
 * @item and returns NULL.  Otherwise does nothing and returns a pointer to the
 * AVL tree node embedded in the previously-inserted item which compared equal
 * to @item.
 *
 * Example:
 *
 * struct int_wrapper {
 *      int data;
 *      struct avl_tree_node index_node;
 * };
 *
 * #define GET_DATA(i) avl_tree_entry((i), struct int_wrapper, index_node)->data
 *
 * static int _avl_cmp_ints(const struct avl_tree_node *node1,
 *                          const struct avl_tree_node *node2)
 * {
 *      int n1 = GET_DATA(node1);
 *      int n2 = GET_DATA(node2);
 *      if (n1 < n2)
 *              return -1;
 *      else if (n1 > n2)
 *              return 1;
 *      else
 *              return 0;
 * }
 *
 * bool insert_int(struct avl_tree_node **root_ptr, int data)
 * {
 *      struct int_wrapper *i = malloc(sizeof(struct int_wrapper));
 *      i->data = data;
 *      if (avl_tree_insert(root_ptr, &i->index_node, _avl_cmp_ints)) {
 *              // Duplicate.
 *              free(i);
 *              return false;
 *      }
 *      return true;
 * }
 */
static AVL_INLINE struct avl_tree_node *
avl_tree_insert(struct avl_tree_node **root_ptr,
                struct avl_tree_node *item,
                int (*cmp)(const struct avl_tree_node *, const struct avl_tree_node *))
{
    struct avl_tree_node **cur_ptr = root_ptr, *cur = NULL;
    int res;

    while (*cur_ptr) {
        cur = *cur_ptr;
        res = (*cmp)(item, cur);
        if (res < 0) {
            cur_ptr = &cur->left;
        } else if (res > 0) {
            cur_ptr = &cur->right;
        } else {
            return cur;
        }
    }
    *cur_ptr = item;
    item->parent_balance = (uintptr_t) cur | 1;
    avl_tree_rebalance_after_insert(root_ptr, item);
    return NULL;
}

/* Removes an item from the specified AVL tree.
 * See implementation for details.  */
extern void avl_tree_remove(struct avl_tree_node **root_ptr,
                            struct avl_tree_node *node);

/* Nonrecursive AVL tree traversal functions  */

extern struct avl_tree_node *avl_tree_first_in_order(const struct avl_tree_node *root);

extern struct avl_tree_node *avl_tree_last_in_order(const struct avl_tree_node *root);

extern struct avl_tree_node *avl_tree_next_in_order(const struct avl_tree_node *node);

extern struct avl_tree_node *avl_tree_prev_in_order(const struct avl_tree_node *node);

extern struct avl_tree_node *
avl_tree_first_in_postorder(const struct avl_tree_node *root);

extern struct avl_tree_node *
avl_tree_next_in_postorder(const struct avl_tree_node *prev,
                           const struct avl_tree_node *prev_parent);

/*
 * Iterate through the nodes in an AVL tree in sorted order.
 * You may not modify the tree during the iteration.
 *
 * @child_struct
 *      Variable that will receive a pointer to each struct inserted into the
 *      tree.
 * @root
 *      Root of the AVL tree.
 * @struct_name
 *      Type of *child_struct.
 * @struct_member
 *      Member of @struct_name type that is the AVL tree node.
 *
 * Example:
 *
 * struct int_wrapper {
 *      int data;
 *      struct avl_tree_node index_node;
 * };
 *
 * void print_ints(struct avl_tree_node *root)
 * {
 *      struct int_wrapper *i;
 *
 *      avl_tree_for_each_in_order(i, root, struct int_wrapper, index_node)
 *              printf("%d\n", i->data);
 * }
 */
#define avl_tree_for_each_in_order(child_struct, root, struct_name, struct_member)     \
    for (struct avl_tree_node *_cur = avl_tree_first_in_order(root);                   \
         _cur &&                                                                       \
         ((child_struct) = avl_tree_entry(_cur, struct_name, struct_member), 1);       \
         _cur = avl_tree_next_in_order(_cur))

/*
 * Like avl_tree_for_each_in_order(), but uses the reverse order.
 */
#define avl_tree_for_each_in_reverse_order(                                            \
    child_struct, root, struct_name, struct_member)                                    \
    for (struct avl_tree_node *_cur = avl_tree_last_in_order(root);                    \
         _cur &&                                                                       \
         ((child_struct) = avl_tree_entry(_cur, struct_name, struct_member), 1);       \
         _cur = avl_tree_prev_in_order(_cur))

/*
 * Like avl_tree_for_each_in_order(), but iterates through the nodes in
 * postorder, so the current node may be deleted or freed.
 */
#define avl_tree_for_each_in_postorder(child_struct, root, struct_name, struct_member) \
    for (struct avl_tree_node *_cur = avl_tree_first_in_postorder(root), *_parent;     \
         _cur &&                                                                       \
         ((child_struct) = avl_tree_entry(_cur, struct_name, struct_member), 1) &&     \
         (_parent = avl_get_parent(_cur), 1);                                          \
         _cur = avl_tree_next_in_postorder(_cur, _parent))

#endif /* _AVL_TREE_H_ */
